Treated highway surfaces



Unite Stats TREATED HIGHWAY SURFACES David P. Spalding, Troy, and Royal V. Mackey, Jr., Scotia, N.Y., assignors to General Electric Company, a corporation of New York This invention is concerned with the treatment of highway surfaces. More particularly, the invention relates to the treatment of highway surfaces byiapplying to the aforesaid highway surfaces a water-soluble, alkali-metal salt of a hydrocarbon-substituted silanetriol.

For brevity, as hereinafter defined in the specification and claims, the term highway surfaces is intended to include, for instance, highways made of concrete, asphalt, gravel, etc., upon which vehicles travel, as well as abutting surfaces which adjoin the highway, such as curbing, sidewalks, various types of railings, such as railings of bridges, safety posts, etc.; streets, roads, alleys, airfields, grade separations, decks of bridges comprising passes over railroad tracks, water, other highways, etc.

Great difficulty has been encountered in the past in connection with highways andsurfaces adjac'entsuch highways. One of the problems inherent in the use of these highway surfaces is the undesirable absorption of light, from either overhead luminaries or of headlights of automobiles, by wet pavements. Persons who have driven over wet pavements, particularly asphaltic or concrete highways, have no doubt noted that a considerable amount of the light generated by their automobile headlights is absorbed by the wet surface of the road, so that an undesirably reduced amount of light is available for driving, making driving conditions subject to increased hazards.

in addition, another highway problem involves undesirable skidding tendencies of automobile tires'on Wet highways. A still further hazard inherent in the use of highways involves the shoulders of the highways, which abut on the hard driving surface. Attempts have been made to buttress the shoulders to make them firm under conditions where they have been completely soaked through or else water has seeped in under the surface of the shoulder so that, in the event a driver must drive onto the shoulder of the road, the shoulder will sustain the car for a sufficient distance to prevent sinking in of the wheels with danger of overturning the car or vehicle.

A still further problem in connection with construction of highways, and particularly concrete highways, is the reduced resitance of such highways to weathering as evidenced by the tendency of the highway surface to fail or spall as a result of the salt chemicals used to hasten thawing and because of the alternate freezing and thawing of the highways in climates where temperatures may drop low enough so that any moisture trapped within the interstices of the concrete or in cracks in the concrete will tend to freeze and cause expansion and further cracking of the highway. This process of freezing and thawing increases the size of the cracks or areas of spalling, permitting larger amounts of water to enter the next time, so that when the water freezes again, a much larger crack develops exposing gravel aggregate as a result of the freezing cycle, thus causing loss of mortar and cansing disintegration of cement or asphaltic concrete pavements.

It is therefore one of the objects of the invention to reduce the skidding of rubber surfaces, e.g., automobile or truck tires, on wet concrete surfaces.

"atent Another object of the invention is to improve the visibility of highways during night driving where light from automobile headlights is reflected from wet highways, and to increase the reflected illumination of lighted highway surfaces when wet.

A still further object of the invention is to improv the resistance of concrete to weathering by minimizing the spalling and cracking of highways and thereby retard disintegration of the highways as a result of alternate thawing and freezing cycles to which the highway surfaces may be subjected.

Another object of the invention is to firm up the shoulders of the highways in times of rain or high moisture conditions, so that undesirable erosion of', the soil and hazardous sinking of vehicular wheels in the shoulder will not occur after such conditions of weathering.

Other objects of the invention will be apparent from the description thereof which follows. i

All the foregoing objects can be attained by coating the highway surfaces with an alkali-metal salt of a hy- 'drocarbon-substituted silanetriol.

The alkali-metal salts employed in the practice of the present invention may be prepared from mono-organosilane triols or their condensation products and are desilicon atom. Additional directions for making these metallic salts (so designated hereinafter to cover the alkali-metal salts of silanetriols) may be found in US. Patent 2,507,200. The resultant aqueous solution con taining the soluble metallic salt is diluted to the desired concentration, partially or completely neutralized, if desired, with such salts as aluminum nitrate, aluminum acetate, etc., as is more particularly disclosed and claimed 3 in Torkelson US. Patent 2,729,572 issued January 3, 1956, and assigned to the same assignee as the present invention. Alternatively, after making the solution with the alkali-metal salt, the latter may be dehydrated partially or completely to give a metallic salt in the formof finely divided powder (if fully dehydrated), which in I turn can be dissolved or dispersed in water or in an alcohol such as methanol, ethanol, isopropanol, etc., and this can be used for application purposes.

The hydrolyzable monohydrocarbon-substituted silane described above may be considered as having the formula RSiX where R is a monovalent hydrocarbon radical, for example, alkyl (e.g., methyl, ethyl, propyl, isopropyl, butyl, hexyl, decyl, etc.); aryl (e.g., phenyl, napthyl, biphenyl, etc.); aralkyl (e.g., benzyl, phenylethyl, etc.); alkaryl (e.g., tolyl, xylyl, etc.); and substituted hydrocarbon radicals; in which the substituent is non-reactive with the hydrolyzable medium or with the alkali-metal hydroxide base used to make the metallic salt. Such substituents are, for instance, halogens, e.g., chlorine, bromine, fluorine, etc. In the above formula, X may be a halogen, for instance, chlorine, bromine, fluorine, etc., an alkoxy radical, e.g., methoxy, ethoxy, propoxy, etc.; amino groups, e.g., the -NH grouping. Preferably X is a halogen, particularly chlorine.

Inorganic bases employed to make the metallic salt are preferably bases of the alkali metals. Among such bases may be mentioned, for example, potassium hydroxide, sodium hydroxide,- cesium hydroxide, etc.

. Patented May 24, 1960 I aee'neeo In making the alkali-metal salt with the hydrocarbonsubstituted silantriol, it is desirable to make it in the form of a metallic salt solution in water in as concentrated a form thereof as practicable. For example, concentrations of the metallic salt ranging from about 10 to 30 percent total solids content (calculated as RSiO M where R has the meaning above and M is an alkali metal, are advantageously preferred. Thereafter, such high concentration solutions can be diluted with water to the desired lower concentrations applicable for treatment of highway surfaces. In some instances, it may be desirable to add small amounts of alcohols, such as ethyl alcohol, propyl alcohol, etc., or -ketones, such as acetone, methyl ethyl ketone, etc., to the'water solution of the metallic salt in order to enhance the stability of such solutions and lower their freezing point, especially when application to highways and surfaces adjoining therewith are to be treated at temperatures below the freezing point of the water. Ethanol is particularly effective and renders the water solution for the alkali-metal salts stable at concentrations ranging from about 1 to 40 percent.

The concentration of the alkali-metal salt in the hydrocarbon-substituted silanetriol employed for treating purposes, for instance, in the form of a water solution, may be varied widely. Generally, we have found that concentrations ranging from 1 to 30 percent of the alkalimetal salt (i.e., calculated as RSi M, where R is a monovalent hydrocarbon radical and M is an alkali metal) are advantageously employed in the form of a water solution. Stated alternatively, the concentration of alkali-metal salt on a weight basis, calculated as RSiO where R is a monovalent hydrocarbon radical, many examples of which are given above, is preferably within the range of from about 0.5 to 20 percent of the total weight of the solids matter in the treating solution. It will, of course, be apparent to those skilled in the art that larger or smaller concentrations of alkali-metal salt may be employed, depending on the conditions of treatment, for instance, type of highway, the properties of the highway and the abutting surfaces desired to be improved, temperature and other environmental conditions, rapidity with which drying is desired (for instance, in treatment of crowded highways, it is often desirable to employ low concentrations of the alkali-metal salt because of the necessity of putting the highway back into service as soon as possible), etc.

The method whereby the alkali-metal salt solution may be applied is relatively simple. In general, it is only necessary to dilute the alkali-metal salt with water to the desired concentration, for instance, from about 0.5 to 20 percent, by weight, of the total weight of the solution, and apply it with a pressure distribution equipment preferably equipped with a series of perforations or nozzles which can cover wide areas as the sprayer moves along the highway surface. The rate of application of the alkali-metal salt solution to the surface of the highways and adjoining areas will vary widely upon such factors as the concentration of the alkali-metal salt, the type of surface to which the latter is being applied, the improvement desired, etc. In general, when applying the alkalimetal salt solution to the highway itself, upon which trucks, automobiles, etc. will travel, we have found that concentrations of about I to 5 percent of the alkali-metal salt (calculated as RSiO can be advantageously used and that from 1 to 5 gallons of such an aqueous solution can be applied per 100 sq. ft. of area treated. Obviously, this condition of treatment can be varied widely, depending upon the various factors recited above.

After treatment of the surface with the alkali-metal salt solution, the surface is allowed to dry undisturbed for anywhere from 15 minutes to about 1 to 2 hours or more, depending upon ambient climatic conditions in order to effect conversion of the alkali-metal salt to an organopolysiloxane surface as a result of the reaction of the carbon dioxide (which supplies the acidic medium for conversion to the organopolysiloxane state) and moisture present in the air with the alkali-metal salt of the hydrocarbon-substituted silanetriol. The desired degree of drying may be judged by determining whether the solution has penetrated the surface and all standing puddles have disappeared.

In general, the conditions of treatment should be such that even distribution of the alkali-metal salt solution on the surface is obtained. This will depend upon the pressure of the applying equipment, the design of the equipment and nozzles, distance from the highway surface, etc., to minimize scattering of the spray. The temperature is advantageously above the freezing point of the liquid medium of the alkali-metal salt solution and may advantageously range from about 10 to 60 C. or more. Although temperatures below freezing may be a condition during which the application of alkali-metal salt solution may take place, attention should be given to preventing freezing of the solution on the surface treated, so that there is no nullification of the advantages of the treatment.

In order that those skilled in the art may better understand how the present invention may be practiced, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

EXAMPLE 1 Methyltrichlorosilane was hydrolyzed by adding it rapidly with stirring to a large excess of water. The amount of water present was substantially in excess of that required to effect complete hydrolysis of all the silicon-bonded chlorine in the methyltrichlorosilane. The resultant solution was allowed to stand until substantially all the formed methylpolysiloxane had precipitated in the form of a fine powder. This powder was filtered from the remaining solution, washed to remove acid, filtered, and dried. The solid gel particles were dissolved by stirring with a 50 percent, by weight, aqueous sodium hydroxide solution. In general, 1 mol of the methylpolysiloxane is allowed to react with about 1 to 1.05 mols of sodium hydroxide to give the alkali-metal salt. The resultant alkaline solution had a total solids content of about 46.7 percent, of which about 14.3 percent was titrated as sodium oxide and contained about 30. percent methylpolysiloxane solids calculated as CH SiO (there being present about 2.4 percent impurities as NaCl and Na CO The composition had a specific gravity of about 1.35 at 25 C. and a pH of about 13. This sodium salt of methyl silanetriol (which is also known as sodium methyl siliconate) is believed to have structure I in dilute aqueous solutions, and it can be dried to a white salt having structure H as its molecular formula:

where .x is a whole number greater than 1.

EXAMPLE 2 The above-described solution of the sodium salt of methyl silanetriol was dissolved in water so that there was obtained a concentration of about a 2 percent solids content, calculated as CH Si0 This solution was then sprayed with a ZOO-gallon sprayer with fan-type nozzles on lanes of a Portland cement concrete highway employing a spray pipe about 11 feet long. For this purpose, there were employed about gallons of the alkalimetal salt solution and it took about 36 minutes to treat an area of about 1658 square yards. The treated area was a two-lane concrete strip of the highway, while an immediately adjacent two-lane strip was left untreated and was used as a control. The treated surface was allowed to air-dry for about an hour, after which traffic was again allowed to go over the lanes. Treatment of the earthen shoulders of the road with the alkali-metal salt solution was also carried out using concentrations of 2,. 5 and 15 percent solids solution calculated as CHgSiO and employing 90 gallons of the alkali-metal salt solution for 2400 square feet of shoulder area. In addition, a complete concrete bridge deck of the highway was treated with the alkali-metal salt solution, including road surface, curbing and sidewalks while an adjacent bridge deck was left untreated as a control.

After treatment of the above surfaces, the areas were permitted to be used in regular traffic and subjected to different weather conditions over a period of four to six months, during which time the surfaces, both treated and an untreated control, were subjected to conditions of heavy trafiic as well as varying Weather conditions of rain, cold, sleet, ice formation, thawing, etc. In the interim, the highway surfaces over which vehicles traveled, including. the bridge deck, were examined at night while still wet from a rain, to determine the advantage of the treatment as far as light reflection was concerned. Where the highway had been treated with the alkali-metal salt solution, from 80 to 100 percent of the light from headlights of cars was reflected while the highway surface which was untreated reflected only one-half the light under the same conditions. Even in the daytime, one could clearly see when observing a wet highway surface where treatment with the alkalimetal salt had been carried out, for the treated wet surface was much lighter in color than was the untreated wet surface, although the appearance of the treated and untreated highway surfaces when dry was essentially the same.

Skidding tests were carried out on the wet highway, on both the treated and untreated portions of the highway surface. It was found that under essentially the same conditions of test skidding of automobile tires (by measuring length of skid of locked wheels), less distance was required to bring a car to a stop on the treated portion of the highway than was required to bring a car to a stop on the untreated portion of the highway. This was entirely unpredictable and contrary to prediction, since organopolysiloxanes in the past had been employed for release purposes. However, under this peculiar combination of conditions, namely, a wet surface of the organopolysiloxane in contact with a rubber tire, skidding apparently was reduced.

With regard to the shoulder treatment of the road with the alkali-metal salt solution, despite many heavy rains, and in spite of the fact that a rain had recently occurred, one could drive the wheels of a car onto the shoulder-treated portion which was firm with only slight sinking in of the wheels in the earth. In addition, it was noticeable that where the shoulder was sloped, the water ran off rapidly, with little if any wetting of the surface. In contrast to this, the untreated shoulders were spongy and showed extreme wetting of the surface and deep penetration by the water. Moreover, evidence of erosion due to the lack of run-off of the water was beginning to appear. In addition, the wheels of the car sank rapidly into the soft shoulder of the watersoaked soil of the shoulder.

With regard to the vertical surfaces of the bridge treated with the alkali-metal salt solution, even when wet, again it was evident that the portions which had been treated were much lighter in color than were the portions which were untreated. An advantage of treatment of vertical bridge surfaces occurs in instances where ferrous metal is in contact with any sections of the concrete sides, and staining occurs on a treated portion of the concrete; under such conditions the stain can be more easily removed than when the staining occurs on an untreated portion. This indicates that treatment with the alkali-metal salt solution can prevent undesirable penetration of stain-bearing water which may course over a treated section of concrete.

The sidewalks of the bridge portion treated with, the

alkali-metal salt solution werealsolighter in color than the untreated portions, and readily shed water, so that any water which did accumulate was in the form of droplets rather than in the form of pools. In addition, there was a greatly reduced amount of wetting of the concrete and, in many instances wherethere was. a slight pitch to the sidewalk surface, the water ran off readily and the sidewalk dried in a relatively short period of time after the rain stopped.

The ability of the alkali-metal salt of thehydrocarbonsubstituted silanetriol, when applied to a concretesurface and allowed to dry and be converted to the organopolysiloxane state to give increased friction against rubber surfaces abraded thereover (thus simulating skidding) where the surface in contact with the rubber was wet with water, was further evaluated as shown in the following tests.

EXAMPLE 3 Concrete slabs were molded from a mixture of ingredients comprising, by weight, 94 parts cement, 223

parts fine aggregate (concrete sand), 425 parts-coarse aggregate (gravel), and 58.4 parts water; These slabs were allowed to age at room temperature (about 30?" C.) for approximately 28 days. slabs were coated with a 2 percent aqueous solution of the sodium salt of methyl silanetriol: (calculated as CH SiO and allowed to air dryi The coefficient of dynamic friction of rubber against the treated surface was measured after 1, 3., 7 and 15 days after application of the alkali-metal salt. The surfaces were ground to equal smoothness before application of the alkali-metal salt solution. The following Table I shows the'coefiicient of dynamic friction after the above intervals after application of the alkali-metal salt solution. The coefficient of friction under similar conditions of an untreated dry slab Based on the formula where f=average coefiicient of friction, V=ve1ocity miles per hour, and S=stopping distance in feet, and

using data from the above table, it was calculated that a car traveling 60 miles per hour would stop in 185 feet on a wet pavement which had previously'been treated with the sodium salt of themethyl silanetriol. andawould require 240 feet to stop on an untreated wet surface.

More precise measurements on the improvementin light reflection from wet concrete surfaces which had previously been treated with an alkali-metal salt of a. hydrocarbon-substituted silanetriol were carried following manner.

EXAMPLE 4 Concrete slabs one-half inch thick were molded from a mixture of ingredients comprising parts cement, 600 parts sand and 100 parts water. These slabs, which were /2 x 3 /2" x 6", were cured for 7 days at 90 percent relative humidity, dried at around 30 C. for 4 days and thereafter dried in an oven to constant weight at C. Each of the slabs was immersed for 30 seconds in a. 2 percent aqueous solution of the sodium: salt of Thereafter, samples of the I out in the e methyl silanetriol (calculated as CH SiO so that only half the slab was immersed, and then allowed to dry for 2 weeks at around 30 C. (room temperature). Thereafter both the treated and untreated portions of the slab were measured for the reflectance of light from different wave lengths as produced by a General Electric Recording Spectrophotometer which sends light through a prism, breaking it down to various wave lengths which are then allowed to impinge upon the treated and untreated portions of the slab. In each instance, the percent reflectance was determined by the machine. The following Table II shows the percent reflectance of light of different wave lengths which is shown in millimicrons.

Table II Percent light reflectance Wave length in mllllmlcrons v Treated Untreated Wet Dry Wet Dry EXAMPLE 5 Cement blocks, 1%" x 3%" x 6" having about a A" lip protruding around the edge of one larger flat surface of the slab so as to give a depression in the form of a dam in the surface of the slab, were prepared from a mixture of ingredientscomposed of 1 part cement (Type IA), 6 parts Calbay sand and 1 part water. After molding of the cement blocks, they were cured in the mold for 24 hours and thereafter for 6 days at 90 percent relative humidity. They were further dried in a 110 C. oven to constant weight. Thereafter, some of the slabs were immersed for 30 seconds in a 2 percent solution of the sodium salt of methylsilanetriol (calculated as CH SiO removed and allowed to dry for several days.

Evidence of penetration of the treating mixture was found as deep as one-quarter inch. The treated and untreated blocks were then filled in the darn portion with 50 cc. water and placed outdoors at a temperature below the freezing point of water. When the water in the darn had frozen, it was thawed by sprinkling 2 grams of calcium chloride on the top and allowing the slabs to remain for id hour until the ice melted. Thereafter, the samples were brought indoors where the temperature was about 30 C., the dammed water was washed with a A jet stream of water (60 p.s.i.) for 10 seconds and the surface condition of the block observed to determine whether particles of sand began to work out of the surface. This alternate freezing and thawing were carried out until the first failure occurred as evidenced by the fact that the above jet of water began to wash out sand from the surface. These tests revealed that the sample treated with the alkali-metal salt of the hydrocarbon-substituted silanetriol did not exhibit failure of the surface until afer an average of 11.3 cycles freezing and thawing. In contrast to this, the surface which had not been treated with the alkali-metal salt solution showed first failure after an average of 5.8 cycles.

It will, of course, be apparent to those skilled in the art that instead of highway surfaces of the type described in the foregoing examples, other types of surfaces, many examples of which have been given above, may be treated with similar advantage. Moreover, the concentration of 8 l alkali-metal salt of the hydrocarbon-substituted silane triol used in the treating solution may be varied widely as pointed out above, and no limiting proportions are intended to be read into the foregoing examples. Obviously, other organic alkali siliconates (alkali-metal salts of other.organosilanetriols), such as potassium methyl siliconate, sodium phenyl siliconate, sodium ethyl siliconate, etc., may be used in place of the sodium methyl siliconate employed in the foregoing examples. In general, the organic alkali siliconates employed in the practice of the present invention may be considered as corresponding to the general formula where R is a monovalent hydrocarbon radical, many examples of which have been given above, and M is an alkali metal. As pointed out above, instead of using aqueous solutions of the metallic salt, it may be desirable to dehydrate the latter to obtain dry compositions of the alkali-metal siliconate and thereafter dissolve the same in an alcohol. Alternatively, alcohol or other suitable solvents miscible with the aqueous alkali-metal salt solution may be added to the aqueous solution for the reasons mentioned previously.

Obviously, other methods of treatment of the highway surfaces and abutting areas may be employed within the scope of the present invention. The highways and adjacent areas treated in accordance with the instant invention have ready utility in the transport of vehicles, whereby driving safety is materially improved, economic advantages are derived in that the effects of harmful forces with which the highway surfaces come in contact are materially reduced and in many respects eliminated, and the appearance of the highways and adjacent surfaces is materially improved and more pleasing to the eye.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. The process for improving the light reflectance of aged Portland cement concrete highway surfaces when wet with water, and improving the weathering resistance of such highway surfaces, which process comprises treating the highway surfaces with an aqueous solution consisting essentially of a water and sodium salt of methyl silanetriol containing from 0.2 to 20 percent, by weight, solids when calculated as CH SiO and allowing the treated surface to dry in contact with air whereby the sodium salt of the methyl silanetriol is converted to a methylpolysiloxane.

2. The process for improving the light reflectance of aged Portland cement concrete highway surfaces when wet with water, and improving their weathering resistance which consists essentially of treating the highway surfaces with an aqueous solution of the sodium salt of a methyl silanetriol which in the presence of carbon dioxide in the air is converted to the methylpolysiloxane state.

References Cited in the file of this patent UNITED STATES PATENTS 2,507,200 Elliott et al. May 9, 1950 2,574,168 Brick Nov. 6, 1951 2,679,491 Kennedy et a1. May 25, 1954 2,683,674 Hatchet July 13, 1954 2,706,724 Bass Apr. 19, 1955 2,803,561 Kather Aug. 20, 1957 OTHER REFERENCES 

